1. Field of the Invention
The present invention relates generally to systems that deliver breathing gases to individuals in need thereof, particularly within a medical context, although other contexts are recognized such as oxygen delivery systems used in high altitude flying.
2. Description of the Prior Art
A very common medical situation is one in which it is necessary to deliver a gas from a gas source to an individual's airway, and, consequently, a large variety of gas delivery systems have been designed for this purpose. Although the prior art of such gas delivery systems is far too copious to inventory here, a representative example may be found in U.S. Pat. No. 4,188,946 to Watson and Rayburn.
Such gas delivery systems comprise at least three necessary elements: 1) a source of the desired gas; 2) a conduit for transmitting the gas from the source to the individual receiving the gas; and, 3) a device for introducing the gas to the airway of the individual. The terms “proximal” and “distal” are used herein in reference to the source; i.e., “proximal” means towards or near the source and “distal” means away from the source; i.e., toward or near the individual receiving the gas.
The source of the gas is normally a tank containing the gas under pressure, or a pump that pumps the gas directly into the system. For the purposes of this invention, a gas outlet built into a wall or bulkhead may also be considered a source. The gas to be delivered is usually oxygen, either alone or admixed with other gases and/or pharmacological agents. A flow-regulator is often provided to control the flow rate of the gas. In some circumstances a demand-valve limits the flow of gas to just the inspiration phase of the person's respiratory cycle; in other circumstances the gas flows freely.
Flexible tubing is generally used as conduits in gas delivery systems, particularly in the distal end of the system. Such tubing is often transparent and made of an elastic material. Depending on the application, the tubing may have an internal diameter ranging from a few millimeters to a few centimeters.
The device for introducing the gas to the individual's airway takes one of a number of forms. One is simply a mask that connects to the distal end of the conduit and covers the individual's nose and mouth simultaneously such that substantially all of the gas entering the individual's airway is that which is delivered by the system. Another device for introducing the gas to the individual's airway is an endotracheal tube, which allows delivery of the gas directly into the trachea of an individual. In other situations it is sufficient to employ a nasal cannula. This is normally a hollow, gas-conducting device having an inlet and two outlets. The inlet of the cannula is attached to the distal end of the conduit and the outlets are placed below the individual's nose such that each of the two outlets is adjacent one of the nares. As long as gas is flowing through the system, the individual inhales an unspecified mixture of the delivered gas and ambient air. If the flow of the gas through the system is cut off, the individual inhales only ambient air, which may not have a sufficiently high oxygen content to sustain the individual.
A means to detect whether or not gas is flowing through the system is an element of existing gas delivery systems that is often critical to the proper operation of the system. Flow-meters and flow-indicators are two means employed to determine whether gas is flowing through a gas delivery system. The standard flow-meter used in medical situations is one that is attached at or near the source of the gas and provides a hollow tube containing a ball in the lumen thereof. The lumen of the tube is in communication with the lumen of the conduit so that gas flowing through the system causes the ball to rise in the tube. The height to which the ball rises in the tube is directionally proportional to the flow rate of the gas. In hospital settings such flow meters are normally attached to a wall behind the individual receiving the gas. In most instances the flow-meter is combined with a flow-valve.
Flow indicators are devices used to visually detect the flow of fluids through conduits without necessarily measuring the rate of flow. A common type of flow indicator is a rotary sight flow indicator, which comprises a rotatable member positioned in a chamber that is in communication with the conduit. The rotatable member is visible through a window in the chamber. When fluid moves through the chamber, it causes the rotatable member to rotate, and this provides a visible indication that the fluid is moving. A representative rotary sight flow indicator is disclosed by U.S. Pat. No. 4,745,877 to Chang.
Such flow indicators are used in gas delivery systems. For instance, U.S. Pat. No. 6,386,196 to Culton discloses a rotary sight flow indicator combined with a flow meter connected to a gas source. Culton also provides a very useful whistle element that gives an audible warning if the conduit should slip off of the flow-indicator while gas is running through it.